We are presently working on the development of 1,3-diyl trapping reactions as useful synthetic processes; trimethylenemethane-type 1,3-diyls are being utilized. We have managed to use the reaction for the efficient synthesis of tricyclopentanoid systems related to diketocoriolin B, hirsutene, and hirsutic acid. Structural modifications of the tricyclopentanoids are being conducted in order to assess structure-activity relationships. We are also using the reaction for the synthesis of pseudoguaianolides such as helenalin. Both of the routes to the (5.3.0) systems which we are exploring use diyl trapping as a key step for the generation of bicyclo (3.3.0) systems. The latter are then rearranged to afford (5.3.0) products.